Osteoporosis is a condition, more common amongst women than men, characterized by deterioration of the bone. The bone becomes porous and brittle. Osteoporosis at present is diagnosed by measuring the density and elasticity of the bone. High density alone does not determine the bone resistance to fracture. The bone can possess quite high density but still be brittle and therefore susceptible to breakage. Prior art methods of measuring bone density do not have the required degree of accuracy to determine small changes in bone density, which is what is needed to establish optimum therapeutic or diagnostic procedures.
Osteomalacia is a condition in which softening of the bone occurs. Softening is the result of absorption of calcium from the bones. It occurs especially in pregnant women and it is believed to be related to a dietary deficiency in vitamin D.
My co-pending U.S. patent application Ser. No. 018,709 filed Feb. 17, 1993 describes and claims an apparatus to measure the physical characteristic of an object. The apparatus has a bath to receive the object and the object can be stabilized in the bath. Liquid is supplied to and from the bath. The temperature of the liquid can be controlled so that it is above the temperature of the object. An ultrasonic transmitter sends a signal through the object and an ultrasonic receiver receives the signal. The velocity of the signal of the object can be calculated. This apparatus is useful in diagnosing osteoporosis.
The heel bone is suited to ultrasonic measurement with its sides relatively parallel. The heel bone is composed mainly of trabecular bone. The elasticity and strength of this bone is provided by its sheet structure. The manner in which trabeculae are assembled is more significant than the volume or any other characteristic of bone. Rigidity and strength is more a matter of geometry than mass. The trabeculae arrangement, and the contiguity that it provides, is a more important parameter than volume or weight for action of hard tissue in determining the stiffness of trabecular bone. Because of these facts the known methods of utilizing the velocity of sound in bone and the attenuation measurements, although appearing to provide sound theoretical methods, have not been satisfactory in diagnosing osteoporosis and are not capable of evaluating the effectiveness of any treatment procedure.
Another difficulty with existing methods is their dependence upon references or standards. Using the standards creates an additive error to any measurement. In addition to this error, the use of standards having homogenous composition is undesirable as these compositions relate poorly to human bone; human bone is a heterogenous material.
X-ray methods have been used to diagnose osteoporosis but have also been found unsatisfactory. They measure only the density and provide no quantitative evaluation of structure. Because they produce ionizing radiation, X-rays are not suitable for this purpose.
No prior art has shown an ability to measure bone structure, density and the velocity of sound in bone using a single device. The use of a single device provides a means of early detection as well as a more accurate assessment of the degree of osteoporosis.
All the present methods depend highly on instrument electronic stability. This can be undesirable. There can also be a lack of uniformity in the transducer characteristic, stemming from the manufacturing process.
Furthermore the accuracy with which the heel can be re-positioned for repeat measurements is not particularly satisfactory in the prior art. The reapplying of the transducer against the heel with the same conditions, particularly the same contact pressure, for subsequent measurements is also not well done in the prior art.